Cable networks are communication networks that communicate broadband communication signals between a centralized headend and a plurality of customer premise devices. Cable networks have many forms, but typically include a dispersed network of coaxial cable. Many cable networks, known as hybrid fiber coax or HFC networks, further include a substantial portion of fiber optic lines.
Historically, cable networks were employed primarily for the delivery of the television program signals. To this end, the cable network headend transmitted a broadband signal to each subscriber through a hierarchical network of coaxial cable, referred to as a cable plant. The broadband signal was divided into a plurality of channels, each channel approximately occupying a 6 to 8 MHz wide band of the overall broadband signal.
The proper operation of cable systems involves field testing, because the cable plant is dispersed throughout the entire cable service area, the network can experience damage or other detrimental phenomena in varied, isolated portions of the network. As a result, many customers may have excellent service, while a few customers cannot receive one or more channels clearly due to a localized problem. Cable service providers have often used handheld signal measurement test equipment to help diagnose problems and perform network analysis.
Various test devices that measured analog cable television channels have been developed, which measure a large number of the channels, and provide a rough spectrum analysis of the cable network. Historically, the test equipment included an RF signal receiver and circuitry for measuring signals received on select channels of the system.
While the cable television system employed analog NTCS standard television signals for years, cable service providers have more recently been switching over to digital television signal broadcasting because of the better cost/service ratios. Accordingly, new digital cable field measurement technologies had to be developed, because many of the field test equipment developed for cable networks was specifically designed to test analog cable television channels. The new digital cable field test equipment typically only measures the signal level available on selected (or all) channels of the cable television system.
As the complexity of cable networks and their test methodologies grows, there is a need for increased access to information by the technicians performing the test. Such information may include details regarding the topology of the network, the level of service of particular customers, and historical test data or data from other test sites.
To address these needs, more and more useful data is stored in the test device. However, there is a limit to the amount of data that may be stored, and the information that a technician may find useful is not always predictable.
An object of the present invention is to overcome the shortcomings of the prior art by providing a test device that uses information generated at a remote modem, in the form of upstream transmission parameters, to generate diagnostic information regarding the upstream transmission channel. In some embodiments, pre-equalization parameters received from a CMTS are used to calculate an upstream phase frequency response and/or group delay.